The invention relates to a method and an apparatus for the adjustment of the working depth of a soil tilling machine.
The attachment of tilling machines to prime movers, such as tractors and/or other hauling devices, has the advantage that the development of traction by the tractor is improved by the force of weight of the entire mechanism and by other forces produced by the tilling machine as the machine moves through the soil. Also, losses, due to the friction developed by the pulled machines, are absent. When moving soil, e.g., when tilling, it is desirable to obtain a uniform working depth during certain operations and thereby achieve a certain soil condition, distribution of the sediment, or to achieve other desirable results.
In the utilization of such a tilling (soil-moving) machine, it is well known to adjust the traction, produced by the tilling machine in the ground in relation to the tractor, and to efficiently utilize the output of the tractor. The traction is adjusted in accordance with the deformation of a measuring spring caused by the degree of traction. The deformation of the spring represents a control value for the adjustment of the working depth. In this view, the degree of traction is utilized in an opposing sense. In homogeneous soil without any variations in slope, a constant value of traction is obtained if a constant working depth is maintained by the tilling machine. However, when the degree of traction changes due to a change of the soil resistance or a change of the slope of the surface being tilled, the working depth of the machine automatically changes.
To minimize the changes in the working depth of the tilling machine, one prior art device utilizes a "mixed adjustment" control, in which, to adjust the relative position of the device with respect to the tractor, an adjustment signal is produced which is composed of a traction signal and of a position signal. The latter signal corresponds to the relative position of the device in relation to the tractor. Depending upon the pre-set or predetermined ratio established between the traction signal and the position signal in the mixing process, the traction adjustment or the position adjustment signal is predominant in this control device. In other situations, when the soil changes, a change of the working depth corresponds to a loss of insensitivity and a loss of velocity in the response to the control inputs. In East German Pat. No. 24 280, a control device is disclosed for the automatic depth adjustment of tilling devices attached to tractors, which particularly relates to plows. The control device includes a traction control and working depth control which is adjustable in relation to the automatic depth control. The control device has a delaying and a counteracting effect and is dependent upon the position between the tractor and the device. With this combined control, a nominal or desired value of traction is set by way of an adjustment of the position and that value changes when the soil resistance changes by slowly following or tracing the deviation from the nominal or desired position value. This control device includes, along with the automatic control system, an integrated control stage and an integrating governor, hence the device tends toward instability. This instability causes a continually variable working depth.
Additionally, West German Pat. No. 29 27 585 discloses an improvement of the mixing control and relates to a method and a device for the adjustment of the working depth. In that device, the follow-up or deviation from the nominal value of the traction is monitored and that follow-up is limited or cut-off in accordance with corresponding changes in the degree of traction or position. However, an adjustment of this kind cannot be theoretically extended because of the many parameters involved, because of their interrelationship and because of the wide range of working conditions. For that reason, the consequences of setting certain limits or nominal values cannot be accurately predicted and further the establishment of those various values to correspond to field working conditions results in greater cost. Hence, the prior art devices teach away from this type of method and/or device.